Copper, nickel, and cobalt are known as valuable metals and used for various applications in industry. Nickel and cobalt are used, for example, for positive electrode materials for secondary batteries. Copper is widely used in electronic materials. Copper serves, for example, as a conductor in electric wires and electronic substrates and as a wiring material within batteries.
In recent years, energy conservation has been strongly promoted, and in the automobile industry, conventional gasoline-engined cars are being rapidly replaced by hybrid cars and electric cars both equipped with secondary batteries using nickel, cobalt, and the like. Nickel and cobalt are scarce resources and most of them depend on imports.
Products which have rapidly spread, such as secondary batteries, can be also easily expected to cause a large amount of waste in the future as used products. Thus, copper, nickel, and cobalt, scarce resources, are treated as waste without recycling of the used products, which is not preferred in terms of resource savings and resource security. Nowadays, the establishment of a method for effectively retrieving valuable metals such as nickel, cobalt, and rare earth metals from such used products is strongly demanded.
The secondary batteries mentioned above include nickel metal hydride batteries and lithium-ion batteries. The positive electrode materials thereof contain manganese as well as nickel and cobalt, which are rare metals. Copper is also used as a constituent of the batteries. In positive electrode materials in the lithium-ion batteries, the content of expensive cobalt is being reduced and the content of less expensive manganese is being increased. Attempts have been recently made to retrieve valuable metals from used batteries, and one of the methods of retrieval is a dry process where used batteries are melted in a furnace and then metal is separated from slag and retrieved. In this process, however, manganese moves into the slag and therefore the only components that are successfully retrieved are copper, nickel, and cobalt.
Also known is a wet process where used batteries are melted in acid and then metal is retrieved by a separation method such as precipitation, solvent extraction, and electrowinning. As a method of precipitation, processes are known where pH adjustment of a solution containing nickel and/or cobalt and manganese is followed by addition of a sulphiding agent to obtain a precipitate of sulphide of nickel and/or cobalt or followed by addition of an oxidizing agent to obtain a precipitate of oxide of manganese (see Patent Document 1). When such a solution also contains copper and/or lead as in the case where waste batteries and other waste electronic components are subjected to acid leaching all at once, the precipitation method described above can be employed to precipitate copper and/or lead as a precipitate of sulphide thereof before nickel and/or cobalt precipitates as a sulphide thereof so as to separate copper and/or lead from nickel and/or cobalt for retrieval. However, the method described in Patent Document 1 has disadvantages such as occurrence of coprecipitation, and therefore it is difficult to completely separate nickel, cobalt, and manganese from each other. The method described in Patent Document 1 has another problem that a small amount of copper, if any, coexisting with nickel and/or cobalt in the sulphide precipitate reduces the purity of the sulphide to make it difficult to perform reuse thereof as battery materials or the like and, as a result, to increase re-refining costs.
As for the case where electrowinning is employed to retrieve nickel as metal, it is known that oxide of manganese, if contained at a high concentration in the system employed, becomes deposited on the anode surface to accelerate anode degradation. Furthermore, in electrowinning, colored fine oxide of manganese typically floats in the electrolyte solution to clog a filter cloth used in electrowinning, to cause contamination of the metal nickel with the oxide of manganese, or to cause another problem, and, as a result, consistent operation becomes difficult to carry out.
In solvent extraction for nickel retrieval, acid-based extraction agents are widely used. However, as described above, manganese is used at a high proportion in positive electrode materials in recent lithium-ion batteries and, accordingly, the melt of the batteries contains manganese at a high concentration. At present, there is no effective extraction agent capable of selectively and effectively extracting nickel from such a system.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2000-234130
Non-Patent Document 1: K. Shimojo, H. Naganawa, J. Noro, F. Kubota and M. Goto; Extraction behavior and separation of lanthanides with a diglycol amic acid derivative and a nitrogen-donor ligand; Anal. Sci., 23, 1427-30, 2007 Dec.